Mechanical apparatus



y 1, 1963 R. E. WILKINS ETAL 3,090,297

MECHANICAL APPARATUS 3 Sheets-Sheet 1 Filed Nov. 17. 1960 F/G. j

. l it: I? I INVENTORS ROBERT E. WILKINS LEONARD EFOWLE BY f v c$ ATTORNEY y 1963 R. E. WlLKlNS ETAL 3,090,297

MECHANICAL APPARATUS Filed Nov. 17, 1960 3 Sheets-Sheet 2 INVENTOR. ROBERT E W/L/(l/VS BY LEONARD E. FOWLE ATTORNEY y 1963 R. E. WlLKlNS ETAL 3,090,297

MECHANICAL APPARATUS Filed Nov. 1'7. 1960 3 Sheets-Sheet 3 INVENTOR. ROBERT E W/LK/MS BY LEONARD E. FOWLE ATTORNEY United States Patent 3,099,297 MECHANICAL APPARATUS Robert E. Wilkins, Wollaston, and Leonard E. Fowle,

Wobnrn, Mesa, assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed Nov. 17, 1960, Ser. No. 69,853 16 Claims. (Cl. 101-93) The present invention relates in general to a new and improved high-speed printer and in particular to a slug actuator assembly for use in a high-speed printer of the kind wherein printing slugs strike the type fonts of a constantly rotating print roll in order to effect printing on an intermediately positioned paper web.

Present-day high-speed printers, for example, printers which are in use with high-speed computers, are frequently called upon to provide a printed output upward of 1,000 lines per minute. Radical departures from conventional printing methods have been required in order to permit printing at this rate. One of the techniques which has found wide acceptance is called on-the-fly printing wherein a constantly rotating print roll has raised type fonts which are struck by type slugs in order to produce an imprint on an intermediately positioned paper web.

Although many improvements have been made since this technique first came into use, the printed output in equipment heretofore available was frequently unsatisfactory, particularly when printed at speeds of the order mentioned above. Unsatisfactory performance shows up primarily in the form of smearing, printing which is too light, and positioning of the printed letters above or below the normal print line. These problems are aggravated where the number of carbon copies which is required is relatively large. Additionally, there are the problems of phantom printing, damage to the paper web and/ or the ribbon and a genera-l lack of reliable performance for long periods of time without shutdown for adjustments or repairs. Where these problems are primarily mechanical in nature, they are often traceable to the slug actuator assembly which, due to its complexity in prior art devices, is critically dependent on a number of adjustments which have a tendency to change during high-speed operation.

Accordingly, it is the primary object of this invention to provide a slug actuator assembly for a hig '-sp'eed printer :which overcomes the foregoing disadvantages.

It is another object of this invention to provide a slug actuator assembly for a high-speed printer which is simple and economical in construction and wherein satisfactory performance is maintained for indefinite periods of high-speed operation.

A precise positioning of the letters on the'print line is possible only if perfect synchronism exists between the rotating print roll and the slug actuator assembly so that the slugs arrive at the print roll at the precise instant when the chosen type fonts are at the print station. 'It is important, therefore, that the timing of the slug travel be accurately controlled. In carrying out the foregoing objectives, it becomes advantageous to employ slugs of relatively low mass which, upon being'linearly accelerated from a predetermined home position, arrive at the print roll under their own momentumandwhich are positively returned to their home position after striking the print roll.

Accordingly, it is a further object of this invention to provide a slug actuator assembly for an on-the-fiy printer wherein the slugs, after arriving at the print roll under their own momentum from a predetermined home position in contact with their respective actuating hammers, are urged back to their home position by a spring.

For printing rates of the order mentioned above, the

angular velocity of the print roll must be high. Since the paper web is stationary during the printing interval while the ribbon moves at its own speed which is less than that of the type fonts, the contact time between the slug and the print roll should be as brief as possible in order to prevent smearing. in order to produce an imprint during this brief interval, a powerful impulse is required which, since the total slug travel is small, must be applied during a relatively short time period. Since the length of the hammer travel is predetermined due to the fact that each hammer starts out in contact with the slug, the conventional Way of raising the force of the hammer blow by materially increasing the length of the hammer travel is precluded. Relatively large solenoids are therefore required to actuate the hammers, the width dimensions of the latter corresponding to those of the side-by-side position'ed slugs. Although slug actuation by means of the hammers may proceed from opposite directions so as to permit successive solenoids to be positioned on opposite sides of the slug module, such an arrangement by itself is inadequate to accommodate the large solenoids required.

Accordingly, it is an additional object of this invention to provide a slug actuator assembly for an on-thefly printer wherein the solenoids which actuate the slug are positioned relatively close to the hammers by placing them along a section of a helix.

Frequently, the number of carbon copies required varies radically in different runs. Under these conditions, it may become desirable to increase the force of the slugs in order to produce clearer printing where many carbon copies are called for, or to decrease it where fewer copies are required in order to lessen the possibility of cutting the paper and/or the ribbon, or of damaging the slugs and the print roll. In the present invention, this may be achieved by controlling the length of the hammer travel and hence the time interval during the forward travel of each slug in which the hammer applies force. This adjustment requires a corresponding change in the solenoid current. Alternatively, the slug impact force may be controlled by adjusting the solenoid current alone.

Accordingly, it is a further object of this invention to provide a slug actuator assembly wherein the force of the slug impact is readily adjustable.

Although simplicity of design with a view to minimizing the number of adjustments which critically affect the operation contributes importantly toward the increased reliability of the slug actuator assembly, additional safeguards are necessary to prevent a sluggish performance or a complete breakdown due to such factors as dirt and paper dust which frequently enter the slug housing in presently available equipment to interfere with the travel. AS previously explained, the printed product may also be affected if the impact of the slugs on the print roll is sufficiently powerful to cause cutting of the intermediately positioned paper and ribbon. While the latter effect may be prevented by adjusting the force of the slug impact, it may not always be convenient to shut down the operation of the printer for this purpose.

Accordingly, it is still another object of this invention to provide a slug actuator assembly in which a protective film is stationed in front of the slugs which prevents the entry of foreign matter into the slug housing while permitting printing to take place through it and which further prevents the paper and ribbon from being cut by the impact of the slug on the print roll.

The various novel features which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification; Fora better understanding of the invention, its advantages and specific objects thereof, reference should be had to the following detailed description and the accompanying drawings in which:

FIGURE 1 illustrates a sub-unit of the slug actuator assembly which shows a slug module positioned opposite the print roll;

FIGURE 2 illustrates an end view of a slug module;

FIGURE 3 illustrates the hammer arrangement for a single slug module;

FIGURE 4 illustrates another sub-unit of the slug actuator assembly which shows the hammers for operating the slugs and their actuating mechanism; and

FIGURE 5 illustrates a portion of the apparatus of FIGURE 4.

With reference now to the drawings, FIGURE 1 illustrates a slug module, partially shown in cross-section, consisting of a pair of separate portions and 12. A slug 14 is visible and is seen to be positioned between the module portions radially with respect to the print roll 42. Since all the slugs are identical, it will sufiice to discuss one slug only. The slug is shown in its home position with the convex slug end 16 bearing against the front surface of one end 18 of a hammer 20. The hammer itself is shown in its inactive position with the rear surface of the hammer end 18 hearing against a hammer stop 22. While the size of the slug is determined by the size of the letters to be printed, as well as by considerations of strength, for certain applications it is preferable to have a slug whose mass is small in order to control the timing of its travel accurately. To this end, metal is removed from the areas 24 and 26, which reduces the mass of the slug without diminishing its strength.

The module portions 10 and 12 are seen to be substantially identical and define the upper and lower surfaces of a slug housing which is completed by a pair of thin partitions 30. These are shown in greater detail in FIGURE 2 which is discussed hereinbelow. Each slug is thus slidably positioned in its own housing to permit linear slug travel in a forward direction (to the left in the drawing) from the home position and return. Contact with the housing walls is made only by the front and rear portions 32 and 34 of the slug. The center slug portion 28 is relieved so as to minimize the friction between the slug and the module portions and the partitions 30 respectively.

The slug 14 contains a slot 36 which extends substantially transverse to the direction of slug travel. A leaf spring 38, which is affixed to the module, extends into the slot 36 where the free end of the leaf spring bears against the rear shoulder 37 defined by the slot. The effect of the spring action is to provide a positive force which urges the slug 14 against the hammer end 18. When the hammer is inactive, i.e. when it is up against its top 22, the home position of the slug is defined. A limit stop 40 extends into the slot 36 and defines the limits of slug travel in the forward and backward directions in the absence of the hammer 20 and of the print roll 42. Specifically, the limit stop prevents the slug from sliding out in a forward direction when the print roll 42 is removed, 'e.g. to insert paper. It further serves to restrain slug travel to the rear to a point where the slug is never beyond the influence of the leaf spring 38. The latter feature not only maintains the slug in a fixed position when the slug module is removed, but it further permits positive positioning of the slug 14 to a home position in the case where the hammer 20 is normally out of contact with the slug.

The striking portion 43 of the slug 14 terminates in a striking surface 44 Whose radius of curvature is slightly larger than that of the print roll 42 and the exposed surfaces of the type fonts 46 on the latter. The mating engagement of the two conforming surfaces thus makes possible clear printing on an intermediately positioned paper web 50 when the slug 14 is impelled against the print roll.

The surfaces 47 of the slug module portions 10 and 12 act as guides for a protective film 48, for the aforementioned paper web 50 and for the ribbon 52, all which pass in front of it. The protective film 48, which may consist of a thin, flexible plastic commercially known as Mylar, passes from a rotatable supply roll 54 across a guide 56 immediately in front of the slug module and in contact with the surfaces 47, across another guide 58 to a film take-up roll 60. The take-up roll is rotatable in the direction of the arrow upon the application of a force to a lever 62 which moves with a ratchet-like action. A parallel linkage 64 transmits the motion of the take-up roll to a temporary film guide 66 which is eccentric with respect to its axis 68. The linkage is shown in its actuated position in heavy lines. Upon removal of the force which is applied to the lever 62, a tension spring 70 returns the linkage 64, the lever 62 and the temporary guide 66 to a rest position which is schematically indicated by means of broken lines in the drawing.

It will be seen from FIGURE 1 that another leaf spring 38' and a limit stop 40 are fastened to the upper module portion 10 from where they extend in a downward direction. From FIGURE 2, wherein a front view of a single slug module is illustrated with the applicable reference numerals, it appears that the last-recited leaf spring and limit stop cooperate with the adjacently positioned slug which is identical with the slug 14 except for the fact that its transverse slot opens upwardly in the drawing and receives the leaf spring 38' and the limit stop 40' from above. The actuating hammer which cooperates with the adjacent slug also extends from above, but is omitted from FIGURE 1 for the sake of clarity. As will become clear from the discussion of FIGURES 3-5 below, the alternate slot positioning which permits slug actuation from two directions is resorted to in order to gain additional space for the hammer actuators.

FIGURE 2 further shows the striking surfaces 44 of the slugs 14 to be aligned in a row at the printing station. The partitions 3t separate successive slugs from each other and define individual slug housings in cooperation with the module portions 10 and 12. The cut-away portion of FIGURE 2 which shows part of the slug module in cross-section illustrates the center portion 28 of the slug which is out of contact with the module portions, as well as with the partitions 30. The limit stops 40 and 40' which extend into the slots of different slugs from below and above respectively, are seen to consist of the extensions of a pair of integral metal pieces 72 and 74 respectively.

FIGURE 3 shows a set of interlaced hammers 20 and 20' of the kind required to operate the slugs of the single module which is illustrated in FIGURE 2. The hammers are seen to extend from below and above respectively, .the hammer ends 18 and 18' being interlaced. Hammer motion occurs respectively in a direction out of the plane of the drawing. As previously pointed out, the interlaced arrangement is dictated by the relatively small width of the individual slugs which makes it diflicult to gain access to all of them from the same direction.

FIGURE 4 illustrates a sub-unit of the slug actuator assembly which is adapted to actuate alternate hammers of the apparatus shown in FIGURE 3 from one direction. Due to space limitations, FIGURE 4 is drawn to a smaller scale than FIGURE 3. Two units of the kind shown are required in order to operate the twelve hammers associated with the slug module of FIGURE 2. In a preferred embodiment of the invention, two brackets, such as bracket 96, are stationed in mirror-image relationship with respect to each other. Six solenoids are stationed on the bracket 96, of which only two are illustrated. The remaining solenoids are schematically indicated by their center lines. Only one of the hammers 20 is visible in the drawing, and is seen to be pivotally disposed about an axis 76. The hammer is shown in its inactive position with the rear surface of the hammer end 18 hearing against the hammer stop 22. The other hammer end 73 is pivotally linked to an armature rod which, in turn,

is affixed to an armature guide 82 of the solenoid. The solenoid further comprises a coil 86 and a cylindrical core 88, as shown. The armature consists of a circular cap 90 attached to the coaxial armature guide 82. which extends into the core 88 where it is movably disposed in an axial direction.

An axial extension 92 of the core 88' threadedly engages a coil adjusting nut 94 which is supported on the bracket 96. The adjusting nut 94 may be rotated against the frictional pressure exerted by :a spring washer 98 to change the axial position of the core 88 with respect to the supporting bracket 96. An extension 106 integral with the core 88 of each solenoid extends into openings 108 in the bracket 96 to prevent rotation of the core when the coil adjusting nut is rotated.

The axial extension 92 is internally engaged by a threaded set screw 100which may be moved axially to vary the pressure exerted on the armature guide 82 by an intermediately positioned compression spring 102. The spring pressure urges the armature in an axial direction to a point where further armature movement is precluded as a result of the interaction 'of the hammer 20 and the hammer stop 22. At this point, a coaxial circular gap 104 is defined between the end surface of the core 88 and the armature 90. The length of the gap 104, which may be of the order of .01 inch, may be adjusted by varying the axial position of the core 88 by means of the coil adjusting nut 94. The gap length determines the extreme forward position of the hammer 20 which is indicated in broken lines in FIGURE 4 and is labeled .105. It is important to note that the slug 14 is able to travel forward beyond the hammer position 105, as shown in the drawing.

The size of the solenoids is largely dictated by the acceleration which is to be imparted to the hammers. For optimum operation, each solenoid should be aligned with its corresponding hammer. The size of the solenoids, however, does not permit of their positioning side by side on a line parallel to the print line. The arrangement which is illustrated in FIGURES 4 and provides a solution to this problem. The shape of the supporting bracket 96 on which the solenoids are stationed is such that it conforms to a section of a helix which is centered about an axis through the pivot of the hammer end 78. Accordingly, the respective solenoids are arcuately positioned side by side, their relative displacement in a direction at right angles to the drawing plane of FIGURE 4 permitting alignment with their corresponding hammers. The radial arc is seen to be centered about the pivot of the hammer end 78. This arrangement provides compactness and simplicity of construction without compromising the efiiciency of operation.

The operation of the slug actuator assembly will now be explained with reference to the drawings. Under normal conditions, when the solenoid 84 is not energized, the spring 1&2 urges the armature guide 82 upwards. This motion is transmitted by the armaturerod 80and rotates the hammer to the rear (clockwise in the drawing), about its pivot 76 until the rear surface of the hammer end 18 bears against the hammer stop 22. As previously explained, this position of the hammer, which is termed the inactive position herein, determines the extreme position of the armature guide 82 and hence of the armature 90. The position of the latterwith respect to the solenoid core 88 determines the length of the gap 104 which, as previously explained, may be adjusted by moving the core 88 in an axial direction. From FIGURE 1 it is seen that the convex slug end 16 bears against the front surface of the hammer end 18 as a result of the force applied by the leaf spring 38. When the hammer is in its inactive position and the slug 14 is in contact therewith, the home position of the slug is defined. In this position, the striking surface 44 of the slug striking portion 43, is seen to be recessed within the module.

Upon the momentary energization of the solenoid in response to an externally obtained signal, the armature is rapidly pulled toward the core 88 against the action of the compression spring 102. The extent of armature motion is determined by the length of the gap 104 and ceases when the armature 90 abuts the end surface of the core 88 to close the gap. This armature movement is transmitted to the hammer 20 and serves toaccelerate the latter forward (counterclockwise in the drawing), from its inactive position to its extreme forward position 105.

The forward hammer motion accelerates the slug 14 forward against the action of the leaf spring '38. The print roll 42 is so positionedthat the forward slug travel is arrested before the rear shoulder 37 of the transverse slot 36 contacts the limit stop 40. It should be noted, however, that the forward slug travel, which may be of the order of .09 inch, exceeds the forward motion of the hammer, which may be of the order of .06 inch. This condition is illustrated in broken lines in FIGURE 4 and causes the slug to arrive at the print roll 42 under its own momentum.

During'the forward movement of the slug, the striking surface 44 presses the Mylar film 48, the paper web 50 and the ribbon 52 against the selected type font 46 which, at that instant, moves through the printing position. Thisaction produces an imprint on the surface of the paper web which faces the ribbon 52.

After the hammer 20 has reached its extreme forward position 1.05 and while the slug is still moving forward,.the action of the spring102 urges the hammer to its inactive position, solenoid energization having ceased. The resiliency of the slug and the print roll produces an impact bounce when the slug strikes the latter. The impact bounce, as well as the action of the leaf spring 38, are instrumental in returning the slug to its home position. Rearward slug travel is now possible due to the return of the hammer to its inactive position. The action of the leaf spring, which urges the slug to the rear, prevents a second or phantom printingwhich may otherwise result due to the impact bounce of the returning slug off the hammer end 18.

It will be apparent from-the foregoing explanation that accurate timing of the entire printing operation is allimportant if theprinted output is to be properly positioned on the print line. To this end, the solenoid 84 is momenta-rily energized a predetermined time interval prior to the instant whenthe selected type font rotates through the printing position. The sequence of events taking place thereafter must. be precisely timed so that the striking surface 44 of the slug 14 reaches the selected type font at the exact inst-ant when the latter is in printing position. The accuracy of the timing is greatly enhanced by the fact that the slug and the hammer are initially in contact with each other at the home position of the slug. Since the home position of the hammer itself is precisely determined, the other steps of the printing squence may be referenced thereto.

In view of th relatively small mass of the slug, the action of the hammer following the initiation of solenoid energization is substantially independent of any factors other than the solenoid characteristic response. The acceleration of the slug is therefore predictable and depends on the force applied by the hammer during the forward travel of *the slug when the latter is in contact with the hammer. The independent movement of the slug during the terminal phase of its'forward travel when only the leaf spring 38 acts on it makes the instant when impact occurs accurately predictable. The. terminal motion of theslug underits own momentum makes the printing independentof theprecise timingof the hammer return to theinaetive position. Moreover, the freedam ofthe slug to bounce back upon impact with the print roll enhances the clarity of the imprint and tends to prevent smearing.

The time interval during which contact between the hammer and the slug is maintained is accurately predictable-by adjusting the gap 104 and/ or the solenoid current.

Accordingly, the acceleration of the slug and therefore its impact face on the print roll, are adjustable to permit clear printing even where the number of the required carbon copies varies.

The force exerted by the spring 102 may be accurately adjusted by means of a set screw 100 so that the hammer will be in its inactive position upon the return of the slug. This is important to the operation of the slug actuator assembly since the impact of the returning slug on a forwardly positioned hammer could conceivably produce phantom printing. Moreover, if successice imprints in the same column position are to be made and the same slug is energiged in rapid succession, it may not start its forward travel from its home position if it encounters the forwardly positioned hammer upon returning to its home position. In such a case, both the timing and the acceleration imparted are different from that obtained when the slug starts out from its home position. Accordingly, the position of the printed letters will, under these conditions, be above the print line due to the premature arrival of the slug at the print roll, and a faint imprint will be obtained due to the inadequate slug acceleration.

The accurate timing of the sequence of events from the instant when the solenoid is energized to the time when the striking surface 44 of the slug arrives at the oppositely positioned type font is important to the proper positioning of the printed characters on the print line. Clearly legible printing without any smearing further requires that the slugs be impelled rapidly against the constantly rotating print roll in order to strike a sharp blow at the intermediately positioned paper web. These objectives cannot be achieved unless dirt and dust, especially paper dust which is created by the impact of the lugs on the papers, is kept out of the individual slug housings so as not to interfere with the free sliding motion of the slugs. The proper performance of the equipment is also affected when the slugs, which move forward at very high velocities, cut the paper and/or the ribbon. Quite apart from the effect such damage has on the equipment and on the printed product, it may generate additional paper dust which, upon entering the housings, will affect the motion of the slugs.

To overcome these problems which frequently cause shutdowns and delays in the operation of conventional high-speed printers, the protective Mylar film 48 is positioned between the slug module and the paper web 50. The Mylar film, while being thin and flexible enough to permit clear printing through it, is sufiiciently strong to withstand repeated pounding by the slugs and need not be continuously moved past the slug module. At infrequent intervals, the Mylar film is advanced to present a fresh section of the slug module. It is important that the aforementioned section of the Mylar film have sufficient slackness to permit forward travel of the low mass slugs in the direction of the print roll without imposing any restraint which affects the timing thereof and/ or the clarity of the printing.

To this end, the motion of the ratchet-like lever 62 in a counterclockwise direction, which produces a similar movement of the take-up roll 60, is coupled to the movement of the eccentric temporary film guide 66 which rotates in the same direction into the direct film path between the guide 58 and the take-up roll 60. The Mylar film which is uncoiled from the supply roll 54 is thus advanced under tension around the temporary film guide 66. After a new film section has been moved into place, the pressure on the ratchet lever 62 is released and the spring 70 moves the linkage 64 in a clockwise direction to its original position which is schematically indicated in broken lines in FIGURE *1. Owing to the ratchet-like motion of the lever 62, this motion is transmitted only to the latter. The clockwise motion of the linkage 64 is further coupled to the eccentric temporary film g i e ich is moved out of the direct path of the Mylar film either entirely, or to a sufficient extent to produce slackness of the film. Since the take-up roll moves in a counterclockwise direction only when it is actuated by the lever 62, there is nothing then to take up this slackness which permits the slugs to move forward without any restraint from the film without affecting the protective function of the latter.

The slug module, as explained above, consists of a pair of separate, substantially identical portions which are readily dismount-ed. This feature permits the operator to load the slugs rapidly into the module whenever a slug is exchanged. Once the limit stops 40 and the leaf springs 38 are set, slugs may be readily interchanged. As previously explained, the presence of the limit stops prevents the slugs from inadvertently sliding out of the module and further prevents each slug from moving beyond the influence of its leaf springs to assure a positive return to its home position.

The invention which forms the subject matter of this application makes possible the accurate positioning of the printed characters on the print line and provides a clean and legible imprint without damage to the paper or to the ribbon, regardless of the number of carbon copies which are printed. Additionally, the apparatus of the invention is simple and economical in construction, it enhances the reliability of the high-speed printer as well as its serviceability and permits long periods of operation without a shutdown for adjustments or repairs.

From the foregoing disclosure of this invention, it will be apparent that numerous modifications, changes and equivalents will now occur to those skilled in the art, all of which fall within the true spirit and scope contemplated by the invention.

What is claimed is:

1. A slug actuator assembly for use in a printer, comprising at least one slug housing, a printing slug disposed in said housing and slidably adapted to have its printing surface protrude :beyond the front of said housing, means for accelerating said slug in a forward direction, a protective film sufficiently thin and flexible to permit slug printing through it, and means for selectively advancing said film under tension past said housing including means for positioning a stationary film section immediately in front of said housing under less tension than said advancing film to prevent a restraint from being imposed on the forward movement of said slug.

2. A slug actuator assembly for use in a printer, comprising at least one slug housing, a printing slug disposed in said housing and slidably adapted to have its printing surface protrude beyond the :front of said housing, means for accelerating said slug in a forward direction, means for positioning a protective film in front of said housing, said film being thin and flexible to permit slug printing through it, said last-recited means comprising a film supply roll rotatably disposed on one side of said housing, a film take-up roll rotatably disposed on the other side of said housing, a pair of fixed film guides disposed on opposite sides of said housing, a temporary film guide eccentrically disposed about its axis of rotation, a linkage coupling said film take-up roll to said temporary film guide, means for selectively rotating said take-up roll to advance said film past said housing, said linkage rotating said temporary film guide into said film path simultaneously with the operation of said take-up roll to advance said film under tension, and means for normally maintaining said temporary film guide at least partially out of the direct film path to provide sufiicient slackness in the filmsection confronting said housing to prevent a restraint fiom being imposed on the forward movement of said s ug.

3. A slug actuator assembly for a high-speed printer of the kind wherein slugs are impelled against a type font-carrying print roll to effect imprints on an intermediately positioned paper web, comprising at least one slug module including a plurality of slug housings respectively open at the front and rear, each of said slugs being slidably disposed in one of said housings opposite said print roll and including a slot transverse to the direction of slug travel, a leaf spring extending into said slot and urging said slug to the rear, a limit stop extending into said slot to confine slug travel in both directions, a hammer positioned rearwardly of each of said slugs and pivoted intermediate its ends, a hammer stop associated with said hammer adapted to bear against the rear surface of one of said hammer ends when said hammer is in its inactive position, said leaf spring urging said slug against the front surface of said one hammer end to define a slug home position when said hammer is inactive, a solenoid corresponding to each of said hammers including an armature, said armature being linearly movable to close a predetermined gap upon the energization of said solenoid, an armature rod affixed to said armature and pivotally linked to the other end of said hammer, spring means urging said armature to an open-gap position determined by said hammer stop, the pivotal hammer motion resulting from the energization of said solenoid being adapted to accelerate said slug in a forward direction from its home position.

4. The apparatus of claim 3 wherein said limit stop confines the rearward slug travel to a point within the range of said leaf spring.

5. The apparatus of claim 3 wherein said slug module comprises a pair of substantially identical detachable portions spaced from each other, each of said slug housings being defined by said spaced module portions and by a pair of parallel partitions disposed therebetween.

6. The apparatus of claim 3 wherein the center portion of each of said slugs is relieved to avoid contact with the walls of said housing.

7. The apparatus of claim 3 wherein each of said slugs ha a concave striking surface adapted to protrude beyond said housing in the forward slug position, said striking surface having a radius exceeding that of said print roll, each of said slugs further having a convex rear surface protruding beyond the rear of said housing in said slug home position.

8. The apparatus of claim 3 and further including means for varying the energizing current of said solenoids to adjust the acceleration of said slugs.

9. The apparatus of claim 8 and further including means for adjusting the length of each of said gaps to arrest the movement of the corresponding hammer before the slug has completed its travel, said spring means being adjustable to return said hammer to its inactive position prior to the return of said slug to its home position.

10. The apparatus of claim 9 wherein each of said solenoids further includes a coil having a cylindrical core, said armature comprising a circular cap coaxially spaced from said core by said spring means to define said gap, an armature guide extending from said armature into said core and movably disposed in the latter, said armature being adapted to abut the end surface of said cylindrical core when said solenoid is energized.

1 1. The apparatus of claim 10 and further including a member engaging the threaded interior surface of an axial extension of said cylindrical core, said spring means being compressed between the facing end surfaces of said member and said armature guide.

12. The apparatus of claim 10 wherein said solenoids are grouped, different groups being positioned on separate supporting brackets, each of said brackets substantially conforming to a portion of a helix centered about an axis through the pivotal links of said other hammer ends.

13. The apparatus of claim 10* and further comprising means positioned on said core for engaging the threaded exterior surface of each of said axial cylindrical core extensions, said last-recited means permitting the axial positioning of each of said cylindrical cores to adjust said gap.

14. The apparatus of claim 3 and further comprising a protective film interposed between said paper web and said slug module, said film permitting slug printing through it and having sufficient slackness to prevent interference with the forward slug travel.

15. The apparatus of claim 3 and further comprising means for positioning a protective film in front of said housing, said film being adapted to permit slug printing therethrough, said positioning means being selectively adapted to advance said film past said housing under tension and to provide sufiicient slackness in the stationary film section immediately confronting said housing to prevent a restraint on the forward movement of said slug.

16. The apparatus of claim 3 and further comprising means for positioning a protective film in front of said housing sufficiently thin and flexible to permit slug printing through it, said last-recited means comprising a supply roll of said film rotatably disposed on one side of said housing, a film take-up roll rotatably disposed on the other side of said housing, a pair of fixed film guides disposed on opposite sides of said housing, a temporary film guide eccentrically disposed about its axis of rotation, a linkage coupling said film take-up roll and said temporary film guide, means for selectively rotating said take-up roll to advance said film past said housing, said linkage causing said temporary film guide to rotate into said film path to advance said film under tension, and means for normally maintaining said temporary film guide out of the direct film path to provide suificient slackness in the film-section confronting said housing to prevent a restraint from being imposed on the forward movement of said slug.

References Cited in the file of this patent UNITED STATES PATENTS 2,787,210 Shepard Apr. 2, 1957 2,849,096 Markes Aug. 26, 1958 2,874,634 Hense Feb. 24, 1959 

1. A SLUG ACTUATOR ASSEMBLY FOR USE IN A PRINTER, COMPRISING AT LEAST ONE SLUG HOUSING, A PRINTING SLUG DISPOSED IN SAID HOUSING AND SLIDABLY ADAPTED TO HAVE ITS PRINTING SURFACE PROTRUDE BEYOND THE FRONT OF SAID HOUSING, MEANS FOR ACCELERATING SAID SLUG IN A FORWARD DIRECTION, A PROTECTIVE FILM SUFFICIENTLY THIN AND FLEXIBLE TO PERMIT SLUG PRINTING THROUGH IT, AND MEANS FOR SELECTIVELY ADVANCING SAID FILM UNDER TENSION PAST SAID HOUSING INCLUDING MEANS FOR POSITIONING A STATIONARY FILM SECTION IMMEDIATELY IN FRONT OF SAID HOUSING UNDER LESS TENSION THAN SAID ADVANCING FILM TO PREVENT A RESTRAINT FROM BEING IMPOSED ON THE FORWARD MOVEMENT OF SAID SLUG. 